The adiabaticity assumption of the vibrationally adiabatic theory of chemical reactions in the zero-curvature approximation is directly tested for the collinear H + H2 reaction against calculations using exact wavefunctions. It is found that the symmetric stretch motion of the transition state is adiabatic to within 10% for total energies E ranging from 0.51 eV to 0.72 eV. For E below the zero-point energy of this symmetric stretch motion non-adiabaticity is substantial and is probably due to tunneling. For E above the first excited vibrational state energy of this symmetric stretch motion the adiabaticity assumption breaks down completely.
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* This work was supported in part by the U.S. Atomic ergy Commission, Report Code No. CALT.-767P4-107. ** Present address: Department of Chemistry, University Houston, Houston, Texas 77004, USA. t Contribution No. 4614.